I could see two ways for this to make sense and be a reasonable encounter power:
1. Hit: on target's next action, they move away from you a number of squares equal to their speed plus your Charisma modifier. They can take no other actions on their turn. They may avoid difficult or hostile terrain, but the movement provokes opportunity attacks normally.
2. Hit: target immediately moves away from you a number of squares equal to their speed plus your Charisma modifier, then are immobilized (save ends). They may avoid difficult or hostile terrain, but the movement provokes opportunity attacks normally.
Either way, it would be a nice encounter power. But if the movement is immediate and they can come right back on their turn, this is a very situationally useful power at best. It could be useful for breaking up a hobgoblin phalanx or for getting an ally out of a flank, but that is about it.